Cook pasta according to package directions. Drain pasta; rinse with cold water. Drain again.
For pasta crust, in a large mixing bowl combine egg, milk, and Parmesan cheese. Stir in pasta. Spread pasta mixture evenly in a greased 12-inch pizza pan. Bake in a 350 degree F oven for 20 minutes.
Meanwhile, in a large skillet cook ground beef, onion, and garlic until meat is brown. Drain fat. Add pepper strips, undrained tomatoes (cut up any large pieces of tomato), and Italian seasoning to meat mixture. Bring to boiling; reduce heat. Simmer, uncovered, for 10 to 12 minutes or until peppers are crisp-tender and most of the liquid is evaporated, stirring once or twice. Stir in mushrooms and crushed red pepper.
Spoon meat mixture over pasta crust. Sprinkle with mozzarella cheese. Bake for 10 to 12 minutes more or until heated through and cheese is melted. To serve, cut into wedges. Makes 6 main-dish servings.